Using water isotopes and SO4/Cl Ratios to investigate the hydrology of wetlands in the Las Cienegas

Erin Gray1, Jennifer McIntosh1, Rachel Tucci1, Ron Tiller2, Andrew Salywon2

1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona

2Desert Botanical Garden, Research, Phoenix, Arizona

Wetlands are surface water systems that support diverse habitats which are frequently integral parts of regional ecosystems. Analysis of water stable isotopes and solute chemistry can reveal the nature and seasonality of the hydrologic connection between wetlands and basin groundwater. This research uses water stable isotopes and sulfate to chloride ratios to investigate the seasonal sources of water and degree of evaporation in wetland complexes (cienegas) and associated surface- and ground-water within the Las Cienegas National Conservation Area (LCNCA) in Southern Arizona. Surface water, springs, and shallow groundwater from piezometers within the multiple cienegas in the LCNCA were sampled seasonally and analyzed. Preliminary results suggest the main source of shallow groundwater and wetlands in the LCNCA is basin groundwater, with little ephemeral input from either direct winter or summer precipitation. There is little evidence of seasonal changes in water source, indicating that basin groundwater sustains these ecosystems year-round. Their apparent reliance on basin groundwater implies that the cienegas may be impacted by increased groundwater pumping.  This insight, as well as the baseline hydrologic data that this research provides, will aid research efforts and help inform future LCNCA management decisions.

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